The favourite in the French presidential election promises to crack down on encryption

This time it's Emmanuel Macron, the favourite to win the French upcoming presidential election.

The independent candidate has attacked big tech firms like Apple, Facebook, and Google over their use of strong encryption in messaging apps, arguing that it aids terrorism.

"Until now, big Internet companies have refused to give their encryption keys or access to this content, saying that they have told their clients that their communications are protected," Macron said, according to TechCrunch. "This situation is no longer acceptable."

Many modern messaging services — like Facebook's WhatsApp, and Apple's iMessage — use strong, end-to-end encryption. This helps keep users' data safe from hackers and prying eyes — but means no-one can else can intercept and read them, even the companies themselves or the authorities with a warrant.

This state of affairs has frustrated many in law enforcement, who fear that terrorists and criminals will make use of them to plot in secret — though security experts counter that it's impossible to introduce a "backdoor" without making the system less secure for everyone.

Now, Macron is signalling that he would pursue a crackdown if elected too.

Speaking at a campaign election on Tuesday, he reportedly warned: "[Terrorist] organisations that threaten us take advantage of the possibilities of modern cryptography to hide their projects. They use strongly encrypted instant messengers to talk with each other and give orders. A good chunk of that internet traffic is encrypted and gets away from police forces. It's obviously a weakness and makes the fight against terrorism harder."

The candidate wants companies to "accept a legal requisition system of their encrypted services similar to the existing one for telecom companies."

Marine Le Pen. Reuters/Jacky Naegelen If he follows through, such a proposal would set the stage for an epic showdown between France and American tech companies.

The major players who use strong encryption have all fiercely defended its use; an open letter on Apple's website from CEO Tim Cook promises customers that "we have never worked with any government agency from any country to create a backdoor in any of our products or services. We have also never allowed access to our servers. And we never will."

France will hold the first round of the presidential election of April 23, with the two candidates with the most votes going forward into a run-off vote on May 7. Far-right Front National candidate Marine Le Pen is ahead in the polls and looks likely to make it into the second round, but Macron is the favourite to win overall.